A syndiotactic polypropylene has been known for a long period of time. Such a conventional polypropylene can be prepared by a low-temperature polymerization in the presence of a catalyst comprising a vanadium compound, an ether and an organic aluminum compound, but it is believed that this kind of polymer is poor in syndiotacticity and has elastomer-like properties. However, these elastomer-like properties are different from inherent characteristics of the syndiotactic polypropylene. In recent years, a polypropylene having good tacticity, i.e., a syndiotactic pentad fraction of more than 0.7 has been discovered for the first time by J. A. Ewen et al. which can be obtained by the use of a catalyst comprising a transition metal compound having an asymmetric ligand and aluminoxane (J. Am. Chem. Soc., 110, p. 6255-6256, 1988).
According to the research of the present inventors, it has been perceived that molded articles obtained by molding a syndiotactic polypropylene prepared through the above-mentioned process, a substantially syndiotactic copolymer of propylene and another olefin, or a mixture of these polymers and a small amount of a substantially isotactic polypropylene in a usual molding manner are relatively excellent in impact resistance but are not satisfactory in point of stiffness.